Wide angle photographic objective of the retrofocus type

ABSTRACT

The wide angle photographic objective of the retrofocus type has the back focus of 0.9 to 1.25 times the focal length of the objective while it has the angle of field of 63* and the relative aperture of F2.8. The objective consists of six lens components the first component of which is a negative meniscus, while each of the second to fourth components is a positive lens element and the fifth component is a negative concavo-concave lens element, the sixth component consisting of two lens elements cemented to each other with the cemented surfaces being convex toward the object, the sixth component having a positive refractive power as a whole. In order to compensate for the aberrations, the objective satisfies the following conditions:

United s Fujii [54] WIDE ANGLE PHOTOGRAPHIC OBJECTIVE OF THE RETROFOCUSTYPE [72] Inventor: Toru Fuiii, Tokyo, Japan [73] Assignee: OlympusOptical Co. Ltd., Tokyo,

Japan [22] Filed: Jan. 20, 1971 [21] Appl.No.: 107,948

[30] Foreign Application Priority Data Jan. 23, 1970 Japan ..'45/5856[52] U.S. Cl. ..350/2l5 [51] Int Cl. ..G02b 9/62, G02b 13/04 [58] Fieldof Search ..350/2l4, 215

[56] References Cited UNITED STATES PATENTS 2,959,100 11/1960Lautenbacher ..350/215 2,844,997 7/1958 Lange ..350/215 X PrimaryExaminer-John K. Corbin Attorney-Kurt Kelman [57] ABSTRACT The wideangle photographic objective of the retrofocus type has the back focusof 0.9 to 1.25 times the focal length of the objective while it has theangle of field of 63 and the relative aperture of F2.8. The

[151 3,682,529 1 Aug. 8, 1972 objective consists of six lens componentsthe first component of which is a negative meniscus, while each of thesecond to fourth components is a positive lens element and the fifthcomponent is a negative concavo-concave lens element, the sixthcomponent consisting of two lens elements cemented to each other withthe cemented surfaces being convex toward the object, the sixthcomponent having a positive refractive power as a whole. in order tocompensate for the aberrations, the objective satisfies the followingconditions:

where f is the focal length of the objective and f f, are the focallength each of the first and second com ponents, a being the air gapbetween the first and second components, d being the thickness of thesecond component, r being the radius of curvature of the rear surface ofthe fourth component, d and d being the air gaps each between the fourthand fifth components and between the fifth and sixth com-' ponents, n.,and n, being the refractive index (d-line) of the front and rear lenselements of the six component.

' 2 Clains, 3 Drawing Figures PATENTEflm 8 m2 SHEET 1 OF 2 INVENTOR TORu. FLLJI I IIOEN T PATENTEDAuc amz 3,682,529 SHEET 2 0F 2 I I d-LINE-"g-LlNE M S 0 2 mm -2 0 2 mm O 2% SPHER'CAL ASTIGMATISM DISTORTIONABERRATION I f=IOO /zs O -2 O 2 mm -2 O 2% SPHERICAL TIGMATISM VDISTORTION ABERRATION AS INVENTOR T'OR, FLLJ'II BACKGROUND OF THEINVENTION The present invention relates to a wide angle photographicobjective of the retrofocus type and, more par ticularly, to a wideangle photographic objective of the retrofocus type having the relativeaperture of F2.8 and the angle of field of 63 with the aberrations suchas the spherical aberration, coma and the distortion and the likeinherent to a conventional retrofocus objective being extremelycompensated for over the entire field of view so that a high resolvingpower is obtained while the back focus of the objective is keptsufficiently great.

In a single lens reflex camera, a long back focus is required for theobjective to be incorporated in the camera due to the requirements inthe mechanical construction of the camera.

When the focal length of a photographic objective of the conventionaltype is made small, the back focus of the objective is made necessarilysmall so that it can not be incorporated in the single lens reflexcamera.

A retrofocus type objective has been developed so as to solve the abovedescribed difficulty. However, the prior art retrofocus type objectivesuffers the flare occurring in the fully opened diaphragm aperture,because the spherical aberration and the coma generated by the concavelens element of high refracting power generally located at the frontside of the objective can not be fully compensated for by the lenssystem located at the rear side of the objective.

The present invention aims at avoiding the above described disadvantageof the prior art retrofocus type objective.

SUMMARY OF THE INVENTION The object of the present invention is toprovide a novel and useful wide angle photographic objective of theretrofocus type which avoids the above described disadvantages of theprior art retrofocus type objective and which has a large relativeaperture and a wide angle of field while the back focus of the objectiveis kept sufficiently great with the aberration being extremelycompensated for over the entire field of view so that a high resolvingpower is obtained.

The above object is achieved in accordance with the present invention byproviding an objective having the relative aperture of F2.8 and theangle of field of 63 and consisting of six lens components, the firstcomponent of which facing to the object consists of a negative meniscus,while each of the second to fourth components consists of a positivelens element and the fifth component is a negative concavo-concave lenselement, the sixth component consisting of two lens elements cemented toeach other with the cemented surfaces thereof being convex toward theobject while the cemented lens elements have a positive refractive poweras a whole, the back focus of the entire system being 0.9 to 1.25 timesthe focal length of the entire system, the objective being characterizedby satisfying the following conditions:

where:

f focal length of the entire system f (1' l, 2, focal length of therespective lens element beginning at the object side ri (i 1,2 radius ofcurvature of the surfaces of the respective lens elements beginningatthe object side :1. (i l, 2, thickness of the respective lens elementand the air gap between the adjacent lens elements beginning at theobject side n, (i l, 2, refractive index of the glass of the respectivelens element with respect to d-line beginning at the object side v, (il, 2, Abbe number of the glass of the respective lens element beginningat the object side By satisfying the above conditions, a high qualityretrofocus type objective is obtained.

If the diverging power of the first component is made great, themarginal light quantity in the peripheral zone of the field of view isincreased and the back focus is made long. However, if the divergingpower is too great, the spherical aberration, the coma, the chromaticaberration of magnification and the like rapidly increase. Thus, whenthe spherical aberration is compensated for by the lens system locatedrearwardly of the first component near the diaphragm of the objective,the non-axial aberrations such as the curvature of field are increased.Therefore, the compensation must be effected by a lens system locatedadjacent to the first component. However, when the compensating lenssystem is located too close to the first component, the back focus isnecessarily made short and the compensation for the coma is madedifficult. Thus, the air gap d between the first component andthesucceeding second component must be kept in the range of d 0.25f.

Under such conditions, the spherical aberration can be extremelyefiectively compensated for by the second component. However, the comais newly generated by the second component thereby deteriorating thequality of the objective. In order to avoid the above defect, therelationship between the refractive power of the first component andthat of the second component must be kept as follows:

By satisfying the above conditions, the spherical aberration as well asthe coma can be appropriately compensated for.

When the thickness d of the second component is made too small, thenon-axial astigmatism is made great. Therefore, the thickness d mustsatisfy the following conditions:

The rear surface of the fourth component is effective for compensatingfor the non-axial astigmatism. However, when the radius of curvature ofthe rear surface of the fourth component is made too small, the coma,particularly the chromatic coma, is remarkably increased. On the otherhand, when the radius of curvature of the rear surface of the fourthcomponent is made too great, the astigmatism is remarkably increased. Inorder to suppress the generation of the coma and the astigmatism, theradius of curvature r of the rear surface of the fourth component mustsatisfy the following conditions:

The generation of the coma is suppressed while the marginal lightquantity is increased as the air gaps ds and d are made small. Thus, theair gaps d and d are required to satisfy the following condition:

The fourth to sixth components inclusive form the so-called Tessar typelens system. Therefore, the nonaxial astigmatism is effectivelycompensated for by increasing the difference (n n between the retractiveindex of the front lens element of the sixth lens components and that ofthe rear lens element thereof. Thus, the difference (n n is required tosatisfy the following condition:

Now, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings illustrating thesame.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinal sectionalview showing the arrangement of the lens components of the embodiment ofthe retrofocus type objective of the present invention;

FIG. 2 shows various aberration curvesof the embodiment of the presentinvention; and

FIG. 3 shows various aberration curves of another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I,the first to fifth lens components are shown by L, to L respectively,while the sixth component is shown as being constituted by lens elementsL and L cemented to each other. The reference symbols r, d, n withsuffixes shown are already referred to in the previous descriptiontogether with symbols f and v with suffixes.

EXAMPLE II f= Angle of field 2w =63 Relative aperture =1:2.8 I r,252.639 d, 5.111 n 1.56883 v. 56.0 r, 45.028 1!, 35.778 n 1.61772 v,49.8 r 128.350 d 20.833 n 1.60342 v 38.0 r. 1299.453 d 0.444 n 1.62041v, 60.2 r, 96.058 d, 5.556 n, 1.6727 v, 32.1 r, 225.911 d, 0.417 n,1.58144 9. 40.7 r, 71.833 d 19.917 n 1.6516 n, 58.5 r.. 107.8l4 d 8.361r, 69.322 d, 2.5 r 52258 d 6.944 r 740.983 d 2.5 n, 218.769 d,. 12.778 r56.236

FIG. 2 shows the various aberration curves of example 1 while FIG. 3shows the various aberration curves of example 11.

It is apparent from the aberration curves shown in FIGS. 2 and 3 thatthe present invention provides a high quality wide angle photographicobjective of the retrofocus type having sufficiently great back focusranging 0.9 to 1.25 times the focal length of the objective.

Iclaim:

1. Wide angle photographic objective of the retrofocus type having sixlens components, the first component of which facing to the objectconsists of a negative meniscus, while each of the second to fourthcomponents consists of a positive lens element and the fifth componentis of a negative concave-concave lens element, the sixth componentconsisting of two lens elements cemented to each other with the cementedsurfaces thereof being convex toward the object while said cemented lenselements have a positive refractive power as a whole, the back focus ofthe entire system being 0.9 to 1.25 times the focal length f of theentire system, wherein the improvement comprises the fact that saidobjective satisfies the following conditions:

where:

f, (i 1,2 focal length of the respective lens element beginning at theobject side.

r, (i= 1,2 radius of curvature of the surfaces of the respective lenselements beginning at the object side d, (i 1,2 thickness of therespective lens element and the air gap between the lens elementsbeginning at the object side n, (i 1,2 refractive index of the glass ofthe respective lens element with respect to d-line beginning at theobject side v, (i 1,2 Abbe number of the glass of the respective lenselement beginning at the object side and the objective satisfying thefollowing numerical data:

f= l angle of fieldZw a 63 Relative Aperture I l'.2.8 r, 56.0l4 d 5.276n, l.56883 v, 56.0 r, 44.446 d, 35.939 n, 1.6l272 v, 58.6 r l32.405 d,23.430 n, 1.607 I 7 v; 40.3 r 525.8 I 3 d 0.567 n 1.62299 u 58.l r,95.025 d, 5.560 n, 1.66998 u 39.3 r, 215.930 d, 0.425 n, l.58 144 v 40.7r, 68409 d, 21.076 n, 1.6516 v, 58.5 r, 99.887 d, 6.666

r l005.378 d 2.496

2. Wide angle photographic objective of the retrofocus type having sixlens components, the first component of which facing to the objectconsists of a negative meniscus, while each of the second to fourthcomponents consists of a positive lens element and the fifth componentis of a negative concave-concave lens element, the sixth componentconsisting of two lens elements cemented to each other with the cementedsurfaces thereof being convex toward the object while said cemented lenselements have a positive refractive power as a whole, the back focus ofthe entire system being 0.9 to 1.25 times the focal length f of theentire system, wherein the improvement comprises the fact that saidobjective satisfies the following conditions:

6 In, n, 0.05

where:

f, (i l,2--) focal length of the respective lens element beginning atthe object side r, (i l,2-) radius of curvature of the surfaces of therespective lens elements beginning at the object side d, (i l,2)thickness of the respective lens element and the air gap between thelens elements beginning at the object side n, (i l,2-) refractive indexof the glass of the respective lens element with respect to d-linebeginning at the object side 1/, (i l,2-) Abbe number of the glass ofthe respective lens element beginning at the object side and theobjective satisfying the following numerical data:

f angle of field 2w 63 relative aperture l:2.8 r, 252.639 r, 45.028 rl28.350 r. 1299.453 r; 96.058 r, 225.9ll r, 7|.833 r l07.8l4 d 8.361 r,69.322 7 d. 2.5 r 52.258 d 6.944 r. 740.983 d 2.5 r 218.769 11,, l2.778r 56.236

t a: a: t

1. Wide angle photographic objective of the retrofocus type having sixlens components, the first component of which facing to the objectconsists of a negative meniscus, while each of the second to fourthcomponents consists of a positive lens element and the fifth componentis of a negative concave-concave lens element, the sixth componentconsisting of two lens elements cemented to each other with the cementedsurfaces thereof being convex toward the object while said cemented lenselements have a positive refractive power as a whole, the back focus ofthe entire system being 0.9 to 1.25 times the focal length f of theentire system, wherein the improvement comprises the fact that saidobjective satisfies the following conditions: 0.5 f1 < f2<5.0 f10.25f<d20.15f< d3<0.3f0.5f< r8 <2.5fd8 + d10<0.2f n6 - n7 < 0.05 where:fi (i 1,2 -) focal length of the respective lens element beginning atthe object side. ri (i 1,2 -) radius of curvature of the surfaces of therespective lens elements beginning at the object side di (i 1,2 -)thickness of the respective lens element and the air gap between thelens elements beginning at the object side ni (i 1,2 -) refractive indexof the glass of the respective lens element with respect to d-linebeginning at the object side Nu i (i 1,2 -) Abbe number of the glass ofthe respective lens element beginning at the object side and theobjective satisfying the following numerical data: f 100angle of field2w63*Relative Aperture 1:2.8r1 156.014d1 5.276 n1 1.56883 Nu 156.0r244.446d2 35.939 n2 1.61272 Nu 258.6r3 132.405d3 23.430 n3 1.60717 Nu340.3r4 525.813d4 0.567 n4 1.62299 Nu 458.1 r5 95.025d5 5.560 n5 1.66998Nu 539.3r6 215.930d6 0.425 n6 1.58144 Nu 640.7r7 68.409d7 21.076 n71.6516 Nu 758.5r8 -99.887d8 6.666 r9 -69.351d9 2.496 r10 46.690d106.808r11 1005.378d112.496 r12 42.055d1212.765 r13 -56.591
 2. Wide anglephotographic objective of the retrofocus type having six lenscomponents, the first component of which facing to the object consistsof a negative meniscus, while each of the second to fourth componentsconsists of a positive lens element and the fifth component is of anegative concave-concave lens element, the sixth component consisting oftwo lens elements cemented to each other with the cemented surfacesthereof being convex toward the object while said cemented lens elementshave a positive refractive power as a whole, the back focus of theentire system being 0.9 to 1.25 times the focal length f of the entiresystem, wherein the improvement comprises the fact that said objectivesatisfies the following conditions: 0.5 f1 <f2<5.0 f1 0.25f< d20.15f<d3<0.3f0.5f< r8 <2.5fd8 + d10<0.2f n6 - n7 < 0.05 where: fi (i 1,2-)focal length of the respective lens element beginning at the object sideri (i 1,2-) radius of curvature of the surfaces of the respective lenselements beginning at the object side di (i 1,2-) thickness of therespective lens element and the air gap between the lens elementsbeginning at the object side ni (i 1,2-) refractive index of the glassof the respective lens element with respect to d-line beginning at theobject side Nu i (i 1,2-) Abbe number of the glass of the respectivelens element beginning at the object side and the objective satisfyingthe following numerical data: f 100angle of field 2w 63*relativeaperture 1:2.8r1 252.639d1 5.111 n1 1.56883 Nu 156.0r2 45.028d2 35.778n2 1.61772 Nu 249.8r3 128.350d3 30.833 n3 1.60342 Nu 338.0r4 1299.453d40.444 n4 1.6204-1 Nu 460.2r5 96.058d5 5.556 n5 1.6727 Nu 532.1r6225.911d6 0.417 n6 1.58144 Nu 640.7r7 71.833d7 19.917 n7 1.6516 Nu757.5r8 -107.814d8 8.361 r9 -69.322d9 2.5 r10 52.258d106.944 r11740.983d112.5 r12 218.769d1212.778 r13 -56.236